Toxic slugs? Neonicotinoid seed treatments in tri-trophic perspective

Neonicotinoid seed treatments are increasingly common in field crop production, but their non-target impacts have not been fully evaluated. For instance, slugs are a key pest in no-till crop production in the mid-Atlantic and Northeast regions of the U.S., but the influence of seed treatments on slug damage has been little investigated. Previous research in wheat and canola indicates that seed treatments can sometimes decrease, but sometimes increase, slug damage to crop plants. We set out to examine the influence of the common neonicotinoid seed treatment, thiamethoxam, on slug damage to soybeans. Using microcosms in the laboratory, we evaluated whether low and high rates of thiamethoxam influenced slug damage to soybean plants. Because previous research indicated that seed treatments are not lethal to slugs at usual doses, we also evaluated whether slugs might pass insecticides to their natural enemies. Using laboratory studies with ground beetles as a model predator, we tested the influence of slug feeding history (untreated, low rate, and high rate thiamethoxam soybean plants) on ground beetles that subsequently attacked them. Our results suggest that neonicotinoid seed treatments do not prevent slug damage to soybean, and in fact may exacerbate slug damage if insecticides are passed to the third trophic level, releasing slugs from their natural enemies.